Seismic activity beneath a Papua New Guinea volcano could mean that a major eruption was imminent, a volcanologist said on Thursday.

Thousands of people have been evacuated from islands surrounding Kadovar Island off the South Pacific nation’s north coast since a volcano there began erupting, spouting ash. Flights nearby have been canceled due to the risk posed by ash plumes and ships were warned to stay away from the island.

Steve Saunders, principal geodetic surveyor at the Rabaul Volcano Observatory in Papua New Guinea, said seismic activity had recently increased beneath the volcano.

“The reason we’re getting activity is probably because new magma is moving up from deeper down,” Saunders told Australian Broadcasting Corp.

Prime Minister Peter O’Neill has said relevant state resources were being made available to support evacuations and he warned northern coastal communities to be alert for possible tsunamis. Kadovar is offshore to the north of New Guinea, the larger island that includes Papua New Guinea’s capital, Port Moresby.

Papua New Guinea sits on the ‘Ring of Fire,’ a line of seismic faults encircling the Pacific that has frequent earthquakes and volcanic eruptions.